1. Field of the Invention
This invention relates in general to hydraulic tools, and in particular to tools for converting energy into a series of rapid, high energy impact blows.
2. Description of the Prior Art
Hydraulic impact tools generally have an energy storage device, such as a coil spring or gas spring, a ram, and a working tool. The energy storage device causes the ram to accelerate to deliver a blow to the working tool. Impact tools are normally used for demolition purposes, such as breaking concrete, pavement, or ice, or for cutting asphalt. These tools can also be used for other jobs, such as compacting soil or driving pipe, posts, or pilings.
One type of impact tool is described in U.S. Pat. No. 4,231,434 (Justus), issued Nov. 4, 1980. In that tool, the ram has a piston portion, which sealingly engages a sleeve to define a piston. Hydraulic pressure pushes the defined piston away from the working tool, to cock the ram, and to store energy by compressing a gas spring. At the top of the stroke, the piston portion of the ram separates from the sleeve, and the ram is accelerated to impact by the gas spring. A coil spring initiates downward movement of the sleeve, and hydraulic pressure returns the sleeve to sealing engagement with the piston portion of the ram.
U.S. patent application Ser. No. 640,728, filed Aug. 14, 1984, shows a hydraulic impact tool having a housing, a working tool, a ram, an energy storage device, and a valve slide. The tool also has a high pressure fluid inlet port, an intermediate pressure fluid inlet port, and a single return line fluid outlet port. The return line fluid outlet is for exhausting fluid from both the upper and intermediate annular chambers in the tool. The tool also has a flow restriction means for restricting the flow of hydraulic fluid between the ram and the valve slide while the ram is moving toward the working tool.